1. Field Of The Invention
This invention relates generally to fibrous webs of enhanced structural integrity and strength, to absorbent articles containing same and to a process for making such fibrous webs. More specifically, the invention relates to a fibrous web having reinforced marginal portions, to absorbent articles such as disposable diapers incorporating same, and to a process for forming reinforced marginal portions in such webs.
2. Description Of The Related Art
In the commercial manufacture of disposable diapers, incontinence garments and similar articles, it is conventional practice to utilize a web of absorbent material sandwiched between a liquid-impermeable backsheet and a liquid-permeable topsheet, the latter of which provides the skincontacting liner of the diaper or other article. Consequently, the liner should be made of a very soft material for the comfort of the wearer. Such soft materials are, however, of low tensile strength, usually comprising a nonwoven web of fibrous material. The backsheet typically is of a liquid-impervious material such as polypropylene or polyethylene sheet material.
With particular reference to disposable diapers, there is typically provided a tape fastener in upper corners of the article, attached to the topsheet and/or backsheet and featuring disposable release strips or alternatively attached at an openable end to a release area of the topsheet. As indicated above, the topsheet or liner typically is a low-tensile strength material, e.g., a spunbonded or bonded carded web liner. Accordingly, a particular problem in the usage of such disposable diaper relates to the tendency of the fixed ends of the fastener tapes to pull out from the corner or "ear" portions of the diaper, on which the fixed end of the fastener tapes are permanently affixed. Such pull-out deficiency is exacerbated by the lack of structural integrity of the topsheet or diaper liner. Although it would appear logical to increase the tensile strength of the liner in order to overcome this problem, increases in tensile strength of the liner material typically are only achieved at the sacrifice of the softness of the liner, which is unacceptable because the liner in use is placed against the skin of the wearer. Although the prior art has proposed a variety of approaches to reinforcement of various portions of disposable diaper articles, such prior approaches can be characterizable by some deficiency, such as manufacturing cost and/or complexity.
U.S. Pat. No. 3,885,566 to E. J. Jacob discloses a disposable diaper comprising a backing sheet of water-impermeable material, a facing sheet (liner) of water-permeable material, and a filling of absorbent material, with pressuresensitive tape fastening strips at the waist portion. The improvement disclosed in this patent is the provision of abhesive and/or reinforcing areas on the liner which serves as a release coat for the adhesive tape strip prior to use. The abhesive may be in the form of an applique of a silicone coating or other release liner permanently adhered to the liner surface. The patent discloses that the appliques may be made of silicone-coated release paper, silicone-coated plastic film, polyvinyl alcohol film, gelatin film, or plastic films generally which are abhesive by themselves without the need for silicone coating, such as plastic films of Teflon.RTM., nylon, cellophane, polyvinylchloride, polyethylene and the like. The attachment of the applique is by any means suitable, such as adhesive bonding, heat-bonding, mechanical bonding, and the like. Water-soluble appliques such as film formers suitably plasticized with water-sensitive to water-soluble plasticizers, such as corn syrup, glycerine, polyglycols and Sorbitol.RTM. are also disclosed. The application of the applique is by coating the entire liner all over, thus insuring that the tape can rest anywhere on the facing sheet, and find an abhesive bed for itself, or for example, by applying the coating in selected patterned areas directly under the tape area. This patent thus discloses an all-over coating or a very limited tape-area coating for the disclosed applique. The all-over coating will, as discussed with reference to the disclosed materials, reduce the hand, or surface feel of the liner as well as increase the manufacturing cost of the diaper article. The tape-area application of the applique does not provide effective reinforcement of the entire ear portion of the diaper article and further, such tape-area applique is employed only on the ear portion of the diaper which provides a release surface for the "free end" of the fastener tape; the other end of the tape is permanently attached to the plastic backing sheet.
U.S. Pat. No. 4,337,771 to H. A. Pieniak, et al describes a disposable diaper having improved fit characteristics about the legs and/or waist of the wearer and having reinforced corners for enhanced securement of the diaper about the wearer. An elongated, inherently elastic ribbon member is positioned along at least one margin of the diaper, secured thereto so as to provide an elastic region at a central portion of the margin and a unitary, relatively inelastic reinforced region in a corner portion of the diaper. The ribbon member, which may be a strip of thermoplastic film, is intermittently secured to the backing and/or facing in the central portion of the diaper margin, and in such region maintains its elasticity. The end portions of the ribbon member may be rendered effectively inelastic by applying heat or other bonding energy to the desired area of attachment. The elastic means and reinforcing means is a member which is elastic in its original state and may be relaxed or have its elasticity rendered ineffective in selected portions by totally heat sealing or ultrasonically sealing those portions to the diaper backing and/or facing. Thus, the ends of the elastic members are treated to remove elasticity, so that when the diaper is relaxed the central portion of each side margin contracts and is elastic while the four corners are non-elastic but are reinforced with additional film material. The ribbon may be sealed as at two sinuous sealing lines to the backing member and the facing layer in the central portion, i.e., to the backsheet and topsheet.
U.S. Pat. No. 4,055,182 to R. J. Mack discloses a disposable diaper comprising an absorbent pad and a relatively thin sheet of flexible material covering a surface thereof. Tape fastener means are provided comprising a pressure-sensitive strip having a section secured to an outer surface of the flexible sheet in an area at least partially covering the pad. Adhesive means directly bond the sheet to the pad in a region extending from such at least partially covered area to a location spaced therefrom in a direction away from forces normally applied to the strip during placement and use of the diaper. This may for example take the form of adhesive applied to the inside of the pad assembly, such as the backing sheet, in order to directly bond the inner surface of the backing sheet to the back surface of the absorbent pad. The adhesive extends throughout a region which includes the area on which the fastener tape is affixed to the backing sheet. The adhesive area extends outwardly from the sides and end of the affixed tape strip. The patent states at column 4, lines 54-59 that the back portion of the absorbent web may preferably be saturated by adhesive throughout such region, such that the adhesive not only bonds the absorbent web to the back sheet, but also acts as a binder for the absorbent web itself. Accordingly, the adhesive is said to substantially increase the strength of the absorbent web, which also enhances the strength of the reinforcement to minimize severance of the backing sheet in the area of the fastening tape. In the disclosed diaper, the backsheet is reinforced, not the topsheet.
U.S. Pat. No. 3,867,940 to F. K. Mesek, et al. describes a multi-layer diaper including a liner, an absorbent web and a water-impervious backsheet. The backsheet is provided with adhesive tabs on its outer surface at its side portions near one end of the diaper and is reinforced with flexible structural material such as scrim, to prevent stretching and rupture of the backing sheet due to tension on the tabs generated during diapering, during the wearing of the diaper, and during its removal. The selected areas of reinforcement include the areas in the vicinity of the tab permanent attachment to the surface of the backing sheet, the front waist portion area, the marginal side portions, or the entire inner surface of the backing sheet. The scrim may be in the form of cotton gauze, polyethylene filament gauze, biaxially oriented polyethylene terephthalate films or other plastic films having a greater modulus of elasticity than the backing sheet. Again, this patent discloses to reinforce the backsheet, with no treatment being described for the topsheet or liner.
U.S. Pat. No. 4,210,144 to H. D. Sarge III, et al. discloses a disposable diaper having a backsheet, a fibrous web absorbent pad, and tape-tab fasteners having free ends which are covered on one surface with a peelable adhesive, so that the free ends can be adhesively secured to an outwardly facing region of the backsheet when the diaper is applied to a user. The disclosed improvement comprises coating on a portion of a surface of the backsheet in the mother's bond region of a material having a relatively high tensile strength and a relatively low elongation to tensile force property whereby the mother's bonds will have increased tensile strength and improved tape-tab peelability/refastenability. Preferably the coated surface is the inwardly facing surface of the backsheet. It is disclosed that a topsheet may be juxtaposed in face-to-face relation with the inwardly facing surface of the mother's bond region of the backsheet and adhesively secured together by a coating of adhesive.
U.S. Pat. No. 4,296,750 to L. S. Woon, et al. discloses a disposable diaper featuring tape closure means and an impermeable backsheet, wherein the areas of the back sheet serving as tape securement zones when the diapers are in use have uniformly adhered to that side of the film facing the diaper interior a layer of hot-melt adhesive, to impart high tear resistance to the diaper article. The hot-melt adhesive has a lower modulus of elasticity than the backsheet material and is applied in heat-softened condition to obtain strong uniform adherence to the film. The hot-melt adhesive layer may be applied across the entire extent (width) of the diaper, or alternatively in separate patches such as shown in FIGS. 4-6 of the patent which constitute the corner portions of the diaper on which the fastener tape is attached. There is no disclosed reinforcement treatment of the topsheet.
U.S. Pat. Nos. 4,069,822 and 4,147,580 to K. B. Buell describe a method of bonding a fluid-porous web to a substrate, wherein the porous web is overall or pattern coated with a hot-melt adhesive onto individual surface fibers and fiber junctions. The fluid-porous web may suitably constitute the topsheet of a disposable diaper assembly, with the topsheet being adhered by the hot-melt adhesive to a substrate which may be the backsheet and/or the absorbent web (core). Since the hot-melt adhesive is applied at only discrete localized points to the fibrous web, the adhesive is substantially invisible and the softness of the product is retained and the moisture permeability reduced only by 5% or less. FIG. 7 in the patent shows a plan view of a porous fibrous web useful as a topsheet in a diaper which is pattern coated for the hot-melt adhesive, in longitudinally extending marginal areas and narrower centrally disposed and spaced-apart longitudinal adhesive bands. The topsheet web is provided with relatively wide glue areas along its longitudinal edges, sized so as to incorporate at least a portion of the side flaps wherein elastic elements are disposed (this region is a partial cut-out to accommodate the legs of the wearer). Between the wide marginal glue areas is a plurality of narrow glue areas extending longitudinally along the web and in parallel spaced relationship. The hot-melt adhesive is applied to individual projecting surface fibers and fiber junctions of the porous web, with hot-melt adhesive globules formed on the individual projecting surface fibers and fiber junctions.